2. Field of the Invention
The subject invention relates to systems for driving tapes and other elongate flexible web-like members and, more specifically, relates to bidirectional tape drives. By way of example, the invention has utility in the magnetic tape recording art.
2. Prior-Art Statement
Dual capstan bidirectional tape drive systems are well known, as is the fact that the leading capstan in such systems is driven at a higher speed than the trailing capstan, regardless of the direction of movement of the tape, so that the ideal of appropriate tape tension between the two capstans is approached as closely as possible. Prior-art approaches to these desiderata have included the use of such equipment as multiple-motor systems, slip clutch arrangements, and spring-biased reel systems.
An advanced dual capstan drive system has been disclosed in U.S. Pat. No. 3,583,618 by Richard A. Lewis. In that system the two capstans are connected, respectively, to first and second drums and are bidirectionally driven via first and second resilient belts which engage both drums and which, respectively, are advanced by first and second pulleys of different diameter. The theoretical background of that system, as well as some practical embodiments thereof, have been described by one of the subject inventors in an article entitlted ASTRODRIVE-A NEW POWER-CONSERVING TAPE DRIVE (Proceedings 1973, International Telemetering Conference).
As that article points out, a basic disadvantage of differential drive-belt systems is a momentary loss of tape tension during tape direction reversals resulting from the inherent elasticity of the drive belts. This in particular limits the use of that system in applications where rapid and frequent shuttling between the forward and reverse mode is required. In an effort to overcome this limitation, it has been proposed that each of the capstan be directly coupled to a separate servo-controlled direct-current motor, and that the relative velocity differential be maintained electronically, rather than mechanically. This, of course, would undo most of the simplicity inherent in the underlying dual resilient belt drive system.
Other disadvantages of the type of tape drive under consideration include a very limited ability to take up slack upon removal of the tape system from the drive, and to limit tension upon insertion of the tape assembly.
A less advanced system of the above mentioned type using individual capstan drives is apparent from U.S. Pat. No. 3,528,625 by Frank C. Bumb.
Other references noted in a novelty search but not considered particularly relevant are U.S. Pat. Nos. 2,873,073, 2,927,743, 3,038,678, 3,050,225 and 3,482,840.